Quoted from ForceFlow:When you do that, all the grit and black dust can get under the mylar and get ground into the playfield.
That's why I clean/wax my Playfield when it looks like it is starting to get dirty and change out the ball. Easy to lift the non adhesive Mylar and clean under them too. Never had any issues with ground in dirt on my Playfields, as a matter of fact, if there was already ground in dirt from previous owners it gets loosened and picked up over time making my playfields look better, not worse for the wear. It's called maintenance and those that don't do it need to get auto cleared playfields which seem like the majority of folks thinking these days.
Just my 2 cents once again.